feat: improve iterator protocol conformance for Test262

[telecos]

Summary

Improve Test262 conformance for the iterator protocol by fixing several spec violations in the bytecode dispatch handlers in dispatch.rs.

Changes

A. for...of / GetIterator (7.4.1):

• Validate that @@iterator() returns an object (TypeError if not)
• Support call-wrapped callable objects as iterator factories

B. IteratorNext (7.4.3):

• Throw TypeError when .next() returns a non-object result
• Support call-wrapped next methods

C. IteratorClose (7.4.6):

• Validate .return() result is an object (TypeError if not)
• Propagate errors from .return() instead of silently swallowing them
• Close generators by marking them as Completed
• Support call-wrapped return methods

D. CreateArrayFromIterable:

• Check @@iterator before falling back to direct .next()
• Throw TypeError for non-object .next() results
• Throw TypeError for null/undefined inputs
• Extract shared collect_from_plain_object_iterator() helper

E. Spread elements:

• Add String, NativeIterator, Generator spread support

F. for...in enumeration:

• Enumerate string character indices

[codecov]

Codecov Report

❌ Patch coverage is 4.67836% with 163 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/stator_core/src/interpreter/dispatch.rs	4.67%	163 Missing ⚠️

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